Teeth Whitening: What Works, What Doesn't, and What Hurts
A clear guide to peroxide chemistry, in-office versus take-home whitening, why charcoal is a bad idea, and which stains will never bleach.
April 7, 2026 · 6 min read · Reviewed by Dr. Marianna Zadov, DDS
How bleaching actually works
Hydrogen peroxide and carbamide peroxide diffuse through enamel into dentin and break apart the large pigment molecules that absorb light. Lighter fragments reflect more light, so the tooth appears whiter. Nothing is stripped from the surface.
Concentration and contact time determine the result. That is the entire mechanism — everything else is delivery method.
In-office versus custom trays
In-office treatment uses high-concentration gel with the gums isolated, delivering a visible change in about an hour. It is the right choice before an event or when you want a supervised jump in shade.
Custom take-home trays use lower concentration over one to two weeks. The final result is comparable and often more stable, and the trays can be reused for touch-ups for years. Many patients do both: an in-office session, then trays for maintenance.
What will not whiten
Crowns, veneers, bonding, and fillings do not bleach. If you whiten natural teeth around old restorations, expect a mismatch and plan to replace them afterward.
Grey tetracycline staining responds poorly and slowly. A single dark tooth after trauma needs internal bleaching or a different approach. Deep intrinsic discoloration is often better solved with veneers than with peroxide.
Sensitivity and the charcoal problem
Transient cold sensitivity is common and usually resolves within a day or two. Pre-treating with potassium-nitrate toothpaste, shortening wear time, or spacing sessions out manages it well.
Charcoal and abrasive whitening powders do not bleach anything. They scrub surface stain while wearing enamel, and thinner enamel reveals more yellow dentin underneath — the opposite of the goal. Whitening supervised by a dentist protects the gums and the enamel while producing an actual color change.
Talk it through with us
This article is general education, not personal dental advice. For a recommendation specific to your mouth, book an exam with Dr. Zadov or read more about our preventive care.